For me it was a tie between Spidey and the X-Men, but a close one. The X-MEN episode NIGHTCRAWLER is IMHO a fantastic episode, featuring a wonderful scene with Nightcrawler and Wolverine about God that I still remember even now.

Difficult decition. I really loved the 3 of them. Hm...Cant pick the first place between "Spiderman" and "X-men". "Ironman" is in second place but by just a milimetric difference.
Maybe "Spiderman" is my fav because it was the cartoon that introduce me to the wonderful world of the wall-crawler. "X-men" had really great animation, character developting and plots. AERRGH!!! Cant decide!!! XD

I'm going to have to say Spider-Man by default, because X-Men had good writing (sometimes) but poor animation (except for a couple episodes), and Iron Man was just terrible all around. Spider-Man had generally decent writing and the animation was always at least better than X-Men.

My favorite was always Spider-man. I don't know what it was, but I was so invested in the plot that I would never miss an episode as a kid. Plus, Spider-man is my favorite superhero and that kinda adds to my bias. X-men was good too and that's my second place. I didn't become a big fan of Iron Man until the movie and I thought the cartoon seemed cheesy as a kid. I saw a little bit of the Hulk and Fantastic Four cartoons and I thought they were alright.